You hear old guitarists like me crap on for hours about how you young YouTubers have it so easy these days with all the resources in the world at your finger tips. Back in my day I'd have to buy a tape with the guitar that I wanted to learn on it. Then listen to the first 2 seconds to try and work out what the guitarist was doing. Stop, then rewind, play. Stop, then rewind, play. Stop, then rewind, play. Stop, then rewind, play. Stop, then rewind, play. Then move onto the next 2 seconds and.... well you get the idea.
So now that there are so many tutorials online this shouldn't be a problem, but you still have to practice the one section you're being shown over and over again (well I do). I used to put the mouse on the video timeline to where I'd want to go back to, then try not to move it when I clicked to play the section again.
I did a bit of Googling and found this Chrome plugin that will loop over and over.
https://www.alvinhkh.com/looperforyoutube
It can be a bit flakey setting the start and end times to loop, but once you've done that it works really well.
I use it all the time now and did so for my #teletuesday Brent Mason solo (here). One really cool feature is that it stores the parameters in the URL so if you get a loop that you're happy with you can just bookmark it.
www.youtube.com/watch?v=44bi8lxcUtM&loop=0&start=00%3A24&end=00%3A52
So this one is for that solo and it will loop forever starting at 24 seconds and going to 52 seconds.
Freakin sweet eh?